DAMAGE ASSESSMENT AND YIELD LOSSES IN SORGHUM DUE TO THE STEM BORER BUSSEOLA-FUSCA (FULLER) (LEPIDOPTERA, NOCTUIDAE) IN NORTHERN NIGERIA

Experiments were carried out at Samaru, Nigeria, during 1981, 1982 and 1983 to determine the relationship between different methods of assessing damage caused by Busseola fusca (Fuller) and the grain weight per head in various local and exotic sorghum cultivars. The sorghum was infested by the naturally occurring populations of the second and third generations. There was no relationship between infestation at 45 days or at harvest and grain weight per head. The relationship between percentage tunnel length and grain weight was variable; in some experiments it was negative and in others positive. Percentage intemodes bored gave a more consistent negative relationship between stem borer damage and grain weight. A newly developed visual damage rating system and nodes bored provided the best relationship to grain weight per head. The lower half of the stalk and the earliest infested gave higher correlations between damage and grain weight than the upper half, especially for nodes bored and the visual damage rating. Sorghum infested before boot formation or plant growth stage 4 or under had greater yield losses than plants infested at later growth stages. Yield loss per head varied between zero and 1.2% per unit of infestation. The results are discussed in relation to previous work on sorghum and corn. © 1990 Taylor and Francis Ltd.